A recombinant human cytomegalovirus (AD169-GFP) expressing green fluorescent protein was generated by homologous recombination. Infection of human fibroblast cultures with AD169-GFP virus produced stable and readily detectable amounts of GFP signals which were quantitated by automated fluorometry. Hereby, high levels of sensitivity and reproducibility could be achieved, compared to those with the conventional plaque reduction assay. Antiviral activities were determined for four reference compounds as well as a set of putative novel cytomegalovirus inhibitors. The results obtained were exactly in line with the known characteristics of reference compounds and furthermore revealed distinct antiviral activities of novel in vitro inhibitors. The fluorometric data could be confirmed by GFP-based flow cytometry and fluorescence microscopy. In addition, laboratory virus variants derived from the recombinant AD169-GFP virus provided further possibilities for study of the characteristics of drug resistance. The GFP-based antiviral assay appeared to be very reliable for measuring virus-inhibitory effects in concentration-and time-dependent fashions and might also be adaptable for high-throughput screenings of cytomegalovirus-specific antiviral agents.Human cytomegalovirus (HCMV), a betaherpesvirus, is a major opportunistic pathogen of humans with a worldwide distribution. Primary infection with HCMV in persons with a normal immune system is generally asymptomatic, while in rare cases a self-limiting, mild mononucleosis syndrome, or even more severe manifestations, may develop. In contrast, in immunocompromised persons (e.g., organ transplant recipients), HCMV frequently causes systemic disease with typical clinical consequences, like retinitis, pneumonitis, or gastroenteritis. The incidence of HCMV disease in AIDS patients, in comparison, has dramatically decreased since the availability of potent antiretroviral therapy. Furthermore, congenital infection is a major problem with HCMV, since this may result in a severe, generalized cytomegalic inclusion disease (CID) of the neonate (reviewed in reference 6).At present, clinically available drugs for antiviral therapy include the inhibitors of viral DNA polymerase, ganciclovir (GCV; also called Cytovene or Cymeven), foscarnet (FOS; also called Foscavir), and cidofovir (CDV; also called Vistide). All these drugs have low oral bioavailability and dose-related toxicities (13, 27); consequently, novel antiviral compounds with improved efficacy and fewer side effects are needed. Currently, several drugs with anti-HCMV activity are in preclinical or clinical evaluations. These include a series of benzimidazole riboside compounds (BDCRB, TCRB, 1263W94, and others) showing efficient inhibition of various steps in HCMV replication (e.g., genomic DNA maturation) (18, 33; reviewed in reference 9). Another attractive inhibitor candidate was described by studies on the phosphorothioate oligonucleotide fomivirsen (ISIS 2922), which specifically binds to sequences complementary to the major...

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The open reading frame UL84 of human cytomegalovirus encodes a multifunctional regulatory protein which is required for viral DNA replication and binds with high affinity to the immediate-early transactivator IE2-p86. Although the exact role of pUL84 in DNA replication is unknown, the nuclear localization of this protein is a prerequisite for this function. To investigate whether the activities of pUL84 are modulated by cellular proteins we used the Saccharomyces cerevisiae two-hybrid system to screen a cDNA-library for interacting proteins. Strong interactions were found between pUL84 and four members of the importin ␣ protein family. These interactions could be confirmed in vitro by pull down experiments and in vivo by coimmunoprecipitation analysis from transfected cells. Using in vitro transport assays we showed that the pUL84 nuclear import required importin ␣, importin ␤, and Ran, thus following the classical importin-mediated import pathway. Deletion mutagenesis of pUL84 revealed a domain of 282 amino acids which is required for binding to the importin ␣ proteins. Its function as a nuclear localization signal (NLS) was confirmed by fusion to heterologous proteins. Although containing a cluster of basic amino acids similar to classical NLSs, this cluster did not contain the NLS activity. Thus, a complex structure appears to be essential for importin ␣ binding and import activity.The nuclear envelope divides eukaryotic cells into a nuclear and a cytoplasmic compartment. This segregation requires specific mechanisms for the continuous transport of large numbers of macromolecules between both compartments. A number of viruses, including herpes-, influenza, and retroviruses, replicate in the host cell nucleus, and thus, as for the cellular macromolecules, viral proteins must traverse the nuclear envelope in order to participate in virus replication (reviewed in reference 58).The nucleocytoplasmic trafficking of proteins occurs through the nuclear pore complex (NPC) and is mediated by an active and selective mechanism that is controlled by saturable transport receptors and the corresponding cisacting transport signals that are termed nuclear localization signals (NLSs) and nuclear export signals (NESs) (reviewed in reference 15). With respect to NLSs the best-characterized transport sequences comprise one or two short stretches of basic amino acids. These basic, generally lysinerich signals are typified by the simian virus 40 (SV40) large T-antigen (TAg) NLS (PKKKRKV) or the cellular nucleoplasmin protein NLS (KRPAATKKAGQAKKKK) and are frequently referred to as classical NLSs. These sequences are recognized in the cytoplasm by a heterodimeric import receptor composed of importin ␣ and importin ␤. Importin ␣, from which six isoforms have been identified in humans (29), functions as an adapter protein between the NLS and the importin ␤ protein. Thus, importin ␣ binds classical NLS-bearing proteins via its two NLS binding sites in the central area (5, 21) and importin ␤ via its amino-terminally located importin ␤-...

The 86-kilodalton immediate-early (IE) 2 protein (IE2-p86) of human cytomegalovirus (HCMV) is a multifunctional regulator of HCMV gene expression which appears to be essential for triggering the lytic replicative cycle. IE2-p86 functions as a promiscuous transactivator of both viral and cellular gene expression and can repress transcription from its own promoter. In this study we demonstrate that a viral early protein, termed pUL84, which is able to interact with IE2-p86 both in vivo and in vitro, modulates IE2-p86 in a specific manner. First, pUL84 acts as a transdominant inhibitor of IE2-p86-mediated transactivation of both homologous and heterologous promoters. Second, negative autoregulation by IE2-p86 is augmented in the presence of pUL84. Using two in vivo assays, we obtained evidence that expression of pUL84 during the IE phase of the viral replicative cycle leads to an inhibition of viral early gene expression which prevents replication of HCMV and results in a persistent infection of UL84-positive cell lines. Transdominant inhibition of a viral IE function by a protein expressed during the later phases of replication appears to be a novel principle used by herpesviruses which could account for the slow replication of HCMV and may be useful in the development of new antiviral strategies.

High-throughput screening in the 1536-well format has been largely restricted to solution-based and cell-based screens. In this article, we show the feasibility of a completely automated, robust scintillation proximity assay in the 1536-well format that is suitable to identify inhibitors for a serine/threonine kinase from a compound library. The introduction of [(33)P]phosphate into a biotinylated peptide substrate mirrors the activity of the kinase. The peptide is immobilized on streptavidin-coated LEADseeker imaging beads and [(33)P]phosphate incorporation is detected with the LEADseeker imaging system of Amersham Pharmacia Biotech. To improve the liquid handling procedures for imaging bead suspensions in the low microliter range, we developed a novel trough with an integrated stirring function. A comparison of the 1536-well assay to a 384-well assay revealed a comparable assay quality with Z' factors of about 0.7 for the 384-well format and 0.6 for the 1536-well format. In an automated screen of a random compound collection, 94.4% of the inhibitory compounds could be identified with both assay formats. Dose-response curves were performed for a selection of identified kinase inhibitors and revealed similar IC(50) values for both assay formats.

Classic PDE5 inhibitors interact with and block the catalytic site of PDE5. They have been clinically validated for treatment of erectile dysfunction as well as reduction of pulmonary arterial pressure, improvement of exercise capacity, quality of life, and arterial oxygenation in patients with secondary pulmonary hypertension. Minor side effects are visual disturbances, headache, migraine, back pain, and interaction with nitrates (hypotension). Some of those side effects presumably can be ameliorated by improving selectivity and pharmacokinetics; other side effects probably are target related due to inhibition of basic physiological processes. Target related side effects may be bypassed by using PDE5 inhibitors with a different mode of action: PDE5, like PDE2, PDE6, PDE10, and PDE11, is a multidomain protein with an N-terminal tandem GAF domain, which in case of PDE5, is allosterically activated by cGMP. Potential inhibitors acting at the PDE5 GAF domain would be expected to inhibit only pathophysiologically upregulated PDE5 activity, whereas basal activity of PDE5 would remain unaffected.Here, we summarize a high-throughput screening campaign to identify inhibitors of the regulatory GAF domain of human PDE5. To target the regulatory domain independently from the catalytic site, we used a chimeric reporter enzyme: The hPDE5 GAF-tandem domain functionally replaced the GAF domain in the cyanobacterial adenylyl cyclase CyaB1. We identified inhibitors that target the GAF domain and also inhibitors that target the bacterial cyclase.Compounds binding to the PDE5 GAF domain were reanalysed with native human PDE5 to demonstrate inhibition using capillary electrophoresis. This identified 16 compounds that act on the GAF domain of PDE5. Two compounds fulfilled the initial requirement to inhibit, exclusively, activated PDE5, but not basal PDE5 activity.

The IE1/2 transcriptional control region of human cytomegalovirus (HCMV) drives the expression of the HCMV major immediate-early genes (UL123-122), which encode proteins crucial for initiation of the virus replicative cycle. Nucleotide sequence polymorphism in this region of the viral genome could account for variations in the replication of HCMV wild-type strains. In order to test this hypothesis, the constitutive transcription-enhancing activity of the IE1/2 transcriptional control region derived from 12 clinical isolates of HCMV was compared. This was done by PCR amplification of the respective elements followed by cloning up-

High-throughput screening in the 1536-well format has been largely restricted to solution-based and cell-based screens. In this article, we show the feasibility of a completely automated, robust scintillation proximity assay in the 1536-well format that is suitable to identify inhibitors for a serine/threonine kinase from a compound library. The introduction of [33P]phosphate into a biotinylated peptide substrate mirrors the activity of the kinase. The peptide is immobilized on streptavidin-coated LEADseeker imaging beads and [33P]phosphate incorporation is detected with the LEADseeker imaging system of Amersham Pharmacia Biotech. To improve the liquid handling procedures for imaging bead suspensions in the low microliter range, we developed a novel trough with an integrated stirring function. A comparison of the 1536-well assay to a 384-well assay revealed a comparable assay quality with Z’ factors of about 0.7 for the 384-well format and 0.6 for the 1536-well format. In an automated screen of a random compound collection, 94.4% of the inhibitory compounds could be identified with both assay formats. Dose-response curves were performed for a selection of identified kinase inhibitors and revealed similar IC50 values for both assay formats.